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<h2><span class="refentrytitle">Macro BOOST_PROTO_EXTENDS</span></h2>
<p>BOOST_PROTO_EXTENDS — For creating expression wrappers that add behaviors to a Proto expression template, like
      <code class="computeroutput"><a class="link" href="boost/proto/extends.html" title="Struct template extends">proto::extends&lt;&gt;</a></code>,
      but while retaining POD-ness of the expression wrapper.</p>
</div>
<h2 class="refsynopsisdiv-title">Synopsis</h2>
<div class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="proto/reference.html#header.boost.proto.extends_hpp" title="Header &lt;boost/proto/extends.hpp&gt;">boost/proto/extends.hpp</a>&gt;

</span>BOOST_PROTO_EXTENDS(Expr, Derived, Domain)</pre></div>
<div class="refsect1">
<a name="id-1.3.32.5.12.7.4"></a><h2>Description</h2>
<p>
        Equivalent to:
        </p>
<pre class="programlisting"><a class="link" href="BOOST_PROTO_BASIC_EXTENDS.html" title="Macro BOOST_PROTO_BASIC_EXTENDS">BOOST_PROTO_BASIC_EXTENDS</a><span class="special">(</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">,</span> <span class="identifier">Domain</span><span class="special">)</span>
<a class="link" href="BOOST_PROTO_EXTENDS_ASSIGN.html" title="Macro BOOST_PROTO_EXTENDS_ASSIGN">BOOST_PROTO_EXTENDS_ASSIGN</a><span class="special">(</span><span class="special">)</span>
<a class="link" href="BOOST_PROTO__1_3_32_5_10_7.html" title="Macro BOOST_PROTO_EXTENDS_SUBSCRIPT">BOOST_PROTO_EXTENDS_SUBSCRIPT</a><span class="special">(</span><span class="special">)</span>
<a class="link" href="BOOST_PROTO__1_3_32_5_10_6.html" title="Macro BOOST_PROTO_EXTENDS_FUNCTION">BOOST_PROTO_EXTENDS_FUNCTION</a><span class="special">(</span><span class="special">)</span></pre>
<p>
      </p>
<p>If the <code class="computeroutput">Domain</code> parameter is dependent, you can specify it as
        <code class="computeroutput">typename Domain</code>, as in
        <code class="computeroutput">BOOST_PROTO_EXTENDS(Expr, Derived, typename Domain)</code>
      </p>
<p>
        <span class="bold"><strong>Example:</strong></span></p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">Expr</span> <span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">my_expr</span><span class="special">;</span>

<span class="keyword">struct</span> <span class="identifier">my_domain</span>
  <span class="special">:</span> <a class="link" href="boost/proto/domain.html" title="Struct template domain">proto::domain</a><span class="special">&lt;</span> <a class="link" href="boost/proto/pod_generator.html" title="Struct template pod_generator">proto::pod_generator</a><span class="special">&lt;</span> <span class="identifier">my_expr</span> <span class="special">&gt;</span> <span class="special">&gt;</span>
<span class="special">{</span><span class="special">}</span><span class="special">;</span>

<span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">Expr</span> <span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">my_expr</span>
<span class="special">{</span>
    <span class="comment">// OK, this makes my_expr&lt;&gt; a valid Proto expression extension.</span>
    <span class="comment">// my_expr&lt;&gt; has overloaded assignment, subscript,</span>
    <span class="comment">// and function call operators that build expression templates.</span>
    <a class="link" href="BOOST_PROTO_EXTENDS.html" title="Macro BOOST_PROTO_EXTENDS">BOOST_PROTO_EXTENDS</a><span class="special">(</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">my_expr</span><span class="special">,</span> <span class="identifier">my_domain</span><span class="special">)</span>
<span class="special">}</span><span class="special">;</span>

<span class="comment">// OK, my_expr&lt;&gt; is POD, so this is statically initialized:</span>
<span class="identifier">my_expr</span><span class="special">&lt;</span> <a class="link" href="boost/proto/terminal.html" title="Struct template terminal">proto::terminal</a><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span> <span class="special">&gt;</span> <span class="keyword">const</span> <span class="identifier">_1</span> <span class="special">=</span> <span class="special">{</span><span class="special">{</span><span class="number">1</span><span class="special">}</span><span class="special">}</span><span class="special">;</span></pre>
<p>
      </p>
</div>
</div>
<div class="copyright-footer">Copyright © 2008 Eric Niebler<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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